Case Report: Left knee pain in a young female athlete

Clinical History

A 14 year old girl was seen in clinic after an injury whilst playing rugby. Although her description was vague, she intimated that a valgus stress had been put on her left leg and described being tackled in rugby practice. She fell on her left knee and heard an audible cracking or ‘pop’ sound, experiencing immediate pain and swelling of the joint. She had no significant past medical history and was taking no regular medication.

On examination, she had a valgus orientation of her leg and was not weight-bearing, with her left knee braced. There were no scars or any obvious swelling of the joint, with no tenderness on palpation. The joint was not hot to touch. She had a full range of active and passive movements, with no associated pain. Lachman’s test and the anterior draw test appeared negative but were difficult to elicit due to the patient guarding her knee and resisting movement. There was no posterior sag. Medial and Collateral ligaments were intact.
X-ray imaging at presentation and later CT imaging (Figure 1) were performed.

1. Based on the history and the following images of her left knee, what the most likely diagnosis?

Explanation

The main differential diagnosis based on presenting complaint is between a ruptured ACL (Option A) or, in light of the patient’s age, a fractured tibial spine (Option C). Excessive tension on the ACL causes rupture of the ligament in adults. However, the relative strength of ligament versus bone [2] in children and adolescents often leads to avulsion fractures of the tibial spine. Mechanically this is usually the result of forceful hyperextension of the knee or a distal blow to the femur with the knee extended [3]; for example, falling from a bicycle, motor accidents and sporting injuries [1] as in this case.

The original plain x-ray on first A & E admission alone was difficult to interpret, hence the CT scan was justified. On x-ray, there is disruption of the articular surface on the medial side and the CT image in the same plane (right) shows the tibial fracture clearly.

2. What is her type of fracture under the Meyer (1959) & Mckeever (1970) classification?

A. Type I – non-displaced
B. Type II – partial displacement, often with anterior hinging
C. Type IIIA - entire eminence out of bed without contact with tibia
D. Type IIIB – as for type A but is also rotated

Answer: B. Type II.

Imaging identified a fracture of the tibial spine, most likely a type II (Option B) as the fragment was only partially displaced and held on in a hinge mechanism

Management

Under general anaesthetic she was found to have a positive Lachman’s test. The procedure was performed arthroscopically. After draining the haemarthrosis and reduction of the fracture, two guide wires were inserted through the fracture fragment. A strong fibre wire suture was passed and wrapped above the fragment to hold it in place (Figure 2).

In some cases this fracture can be reduced under a general anaesthetic [1,4] and providing it allows full extension of the knee can be immobilised in plaster for 6 weeks. The difficulty with this technique occurs when the menisci impinge on reduction [1]. Operative repair is now generally done with the use of arthroscopy, this is usually achieved with the aid of temporary stabilisation with a k-wire (obliquely placed) and fixed in place with sutures, or alternatively with a short screw which does not cross the epiphyseal plate [1]. Indications for surgery are ligament instability [1] (however follow-up in some studies show no difference in surgical versus non-operative management [1]).

Outcomes

The patient was placed in extension and the leg immobilised with a backslab to be held in place for two to three weeks (non-weight bearing). After this she will be given a brace for six to eight weeks and during this period gradual weight bearing will be started. Once out of brace she will commence an ACL rehabilitation programme, with the final outcome being known at about 6 months post-surgery. It is likely (with adherence to the rehabilitation programme) that this patient will return to pre-injury levels of activity.

3. Which of the following is the commonest long-term complication in such a patient?

Figure 2. X-rays taken after surgery AP (right) and lateral (left) show that the fracture fragment has been reduced.

Answer: B. Laxity

Explanation

Of the above listed complications, the most common is laxity, (Option B) with up to 64% of patients having some anterior instability in one study after four years of follow up [5]. This is particularly the case if the fracture was partially or fully displaced [6]. However, in the majority of cases this is not severe enough to require treatment [1], and only around 10% of patients in the study were troubled by laxity subjectively [5]. There is little difference in functional outcome with conservative and operative management [5,6,7].

With early diagnosis and treatment in these patients outcomes are very good [6] and very few cases result in degenerative change [7]. Mal-union (which may lead to a fixed flexion deformity) is a rare complication largely due to the good blood supply the fragment receives from the vessels of the anterior cruciate ligament [7].

Case Learning Points

• Tibial spine fracture is more common than rupture of the anterior cruciate ligament in children and young adults, due to the relative strength of ligaments versus bone.
• This injury may be difficult to spot on plain film radiographs.
• Outcomes are good whether managed surgically or conservatively, with the most common complaint in long-term studies being laxity.